Hydraulic pump or motor having a rotary cylinder barrel

ABSTRACT

A hydraulic pump or motor having a rotary cylinder barrel for axially reciprocating pistons for use with externally supplied fluids comprising a housing, a rotating cylinder barrel mounted slidably only in the axial direction on a drive shaft secured within said housing, an inclined swash plate at one end of said housing for regulating the reciprocating of pistons disposed within the pumping chambers of said barrel, a valve plate interposed between the other end of said barrel and the internal forward portion of said housing in slidable contact therewith, said valve plate having slots for the passage of low pressure and high pressure fluids therethrough and oscillating at the coacting surfaces of the cylinder barrel and the valve plate itself. The valve plate is further provided with means compensating the tilting moment acting on said valve plate, said compensating means including at least one balancing piston movably positioned to a radius direction of said valve plate and being operated by pressure fluid delivered from said slot positioned at the high pressure side of said valve plate during rotation of said barrel, and thereby assuring the fluid sealing between said co-acting surfaces.

United States Patent Kobayashi et al.

[54] HYDRAULIC PUMP OR MOTOR HAVING A ROTARY CYLINDER BARREL [72] Inventors: Akira Kobayashi, Nagoya; Mlyao Takayuki, Toyota, both of Japan [73] Assignee: Kabushiki Kaisha Toyota Chuo Kenkyusho, Nagoya-shi, Aichi-ken, Japan [22] Filed: June 5, 1970 21 Appl. No.: 43,712

[30] Foreign Application Priority Data June 9, 1969 Japan ..44/45309 [52] U.S. Cl. ..91/485, 91/487 [51] Int. Cl ..F01b 13/04 [58] Field olSearch ..91/485, 48,499

[56] 1 References Cited UNITED STATES PATENTS H 2,525,498 10/1950 Naylor et al.. ..9l/485 3,398,698 8/1968 Eickmann.., ..9 1/485 FOREIGN PATENTS OR APPLICATIONS 725,959 1/1966 Canada ......91/435 [151 3,657,970 [4 1 Apr. 25, 1972 Great Britain ..9 H485 4/1960 Great Britain ..9 H485 Primary Examiner-William L. Freeh Attorney-Berman, Davidson and Herman 57] ABSTRACT A hydraulic pump or motor having a rotary cylinder barrel for axially reciprocating pistons for use with externally supplied fluids comprising a housing, a rotating cylinder barrel 'mounted slidably only in the axial direction on a drive shaft secured within said housing, an inclined swash plate at one end of said housing for regulating the reciprocating of pistons disposed within the pumping chambers of said barrel, a valve plate interposed between the other end of said barrel and the internal forward portion of said housing in slidable contact therewith, said valve plate having slots for the passage of low pressure and high pressure fluids therethrough and oscillating at the co-acting surfaces of the cylinder barrel and the valve plate itself. The valve plate is further provided with means compensating the tilting moment acting on said valve plate, said compensating means including at least one balancing piston movably positioned to a radius direction of said valve plate and being operated by pressure fluid delivered from said slot positioned at the high pressure side of said valve plate during rotation of said barrel, and thereby assuring the fluid sealing betweenrsaid co-acting surfaces.

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ATTORNEYS.

INVENTORS.

HYDRAULIC PUMP OR MOTOR HAVING A ROTARY CYLINDER BARREL This invention relates to hydraulic power transmission devices and more particularly to fluid pumps or motors with a rotary cylinder barrel for pistons to axially reciprocate.

In the pumps or motors of the type, the pump or motor actions are produced by the discharge and charge of pressure fluids at the co-acting surfaces of the valve plate secured within the housing and the rotating cylinder barrel secured on a drive shaft journaled within the housing. Recognized generally, however, is the fact that the precise-angle contacts cannot be assured between the drive shaft and the valve plate face and also between the valve plate face and the cylinder barrel face by the accidental errors in the manufacturing and assembling works of the cylinder barrel and the valve plate, or the bending of the drive shaft caused by counteracting forces through the pistons from the inclined swash plate regulating the reciprocating motion of the pistons in high pressure operations of the device. This causes the irregular contact of the cylinder barrel to the valve plate as the device is operated in higher speeds or higher pressures and poorer fluid sealing at said co-acting surfaces.

It has, therefore been proposed heretofore to have either the cylinder barrel or the valve plate mounted oscillatably on the drive shaft so as to create smooth contact between the cylinder barrel and the valve plate, which gives certain allowances to the fluid sealing to unify the pressure contact between the cylinder barrel and the valve plate. For instance, provided is such a device as having the cylinder barrel mounted at one point on the drive shaft to realize automatic adjustments for proper fluid sealing at the co-acting surfaces of the cylinder barrel and the valve plate. In the device with the cylinder barrel movable on the drive shaft, however, the oscillation of the cylinder barrel increases easily more than necessary in the high speed operations or when the barrel is made in a Iargersize.

Another device has been proposed, in which the cylinder barrel is secured non-movably on the drive shaft and a spherical seat is provided to hold the valve plate inside the housing. The contacting surface of the valve plate is made in a matching spheric curve to said spheric seat so that the valve plate can have free sliding movements on the spherical seat to secure constantly close contact of the cylinder barrel face and the valve plate face. In this instance, however, the operation fluid pressure between the high pressure side of the spherical face of the valve plate and the corresponding portion of the spherical seat produces tilting moments to press the valve plate to the low pressure side from the high pressure side, the valve plate tilting toward the cylinder barrel contacting face along the said spherical seat of the housing. This makes it impossible to maintain fluid sealing at the co-acting surfaces of the cylinder barrel and the valve plate and this phenomenon becomes more remarkable as the device is operated at higher pressures.

It is, therefore, a primary object of this invention to provide a versatile rotary device capable of efliciently performing as either a pump or motor under a variety of operating conditions.

Another object of this invention is to provide a hydraulic pump or motor having a rotary cylinder barrel for axially reciprocating pistons capable of operating at high rotative speeds and high pressures with a minimum of fluid and torque losses.

Another object of this invention is to provide a hydraulic pump or motor having a rotary cylinder barrel for axially reciprocating pistons with means compensating the unbalancing moment acting on a valve plate, said means operating by the pressure fluids from either slots for the passage of low pressure and high pressure fluids therethrough, thereby assur' ing the fluid sealing between said co-acting surfaces.

In brief, in the preferred embodiment of this invention, a rotating cylinder barrel is slidably only in the axial direction on a drive shaft secured within a housing along the longitu dinal direction therein. A valve plate is interposed between the one end of said barrel and the internal forward portion of said housing in slidable contact therewith, said valve plate having a spherical surface on said co-acting surface and slots for the passage of low pressure and high pressure fluids therethrough. The valve plate is further provided with means compensatingthe unbalancing moment acting on said valve plate, said compensating means comprising a pair of pistons operating directly or indirectly toward. the outer round edge of said valve plate by the pressure fluids from either of said slots. Thus, it is now recognized that regardless the manufacturing and/or assembling errors of the cylinder barrel and the valve plate, precise contact of the barrel face and the valve plate face can be maintained and any unbalancing or tilting moment caused by the increase of the barrel size and the high pressure operation of the device can properly be compensated to produce smooth contact of the cylinder barrel and the valve plate.

Other objects and advantages of this invention should be readily apparent by reference to the following specification, considered in conjunction with the accompanying drawings forming a part thereof, and it is to be understood that any modifications may be made in the exact structural details there shown and described, without departing from or exceeding the spirit of the invention.

In the drawings;

FIG. 1 is a longitudinal transverse cross-sectional view of a rotary pump or motor having axially reciprocating pistons comprising the subject matter of the invention;

FIG. 2 is a vertically cross-sectional view taken along the line 2-2 in FIG. 1;

FIG. 3 is a cross-sectional view taken on the line 3-3 of FIG. 1, looking in the direction of the arrows;

FIG. 4 shows a modified form of the arrangement of compensating pistons shown in FIG. 3;

FIG. 5 is a longitudinal transverse cross-sectional view of a modified embodiment of this invention;

FIG. 6 is a cross-sectional view taken on the line 6-6 of FIG. 5, looking in the direction of the arrows;

FIG. 7 is a longitudinal transverse cross-sectional view of a further modified embodiment of this invention; 7

FIG. 8 is a cross-sectional view taken along the line 8-8 in FIG. 7, showing compensating pistons;

FIG. 9 shows a still further modified embodiment of this invention;

Corresponding parts are provided throughout the figures with similar reference numerals.

FIGS. 1, 2 and 3 are to show one preferred embodiment of the instant invention. A cylinder barrel 5 is mounted on a drive shaft 1 journaled within a housing 4 through a bearing 2 and a sleeve 3. The cylinder barrel 5 is provided with a plurality of cylinders or pumping chambers 6 having their center axes in parallel to the drive shaft 1, and engaged reciprocatably in the pumping chambers 6 are a corresponding number of plungers or pistons 7. An. inclined swash plate 9 is secured at its right and left edges on the housing 4 and the angle adjustment of the swash plate 9 is done by an actuator connected to the lower portion of the swash plate 9, the actua tor being omitted in the drawings. The top portions of the pistons 7 make sliding motion on the surface of the swash plate 9 through piston shoes 8 engaged in a guide member 8a rotating with the drive shaft 1.

A key 1a fixed on the drive shaft 1 prevents the cylinder barrel 5 from rotating with respect to the drive shaft 1, the cylinder barrel 5 yet being mounted slidably in the axial direction on the drive shaft 1. A biasing coil spring 13, positioned on the drive shaft 1 between a flange l2 thereon and a sleeve 11, acts on the cylinder barrel 5, thereby keeping the outer face 5a in sliding contact with the face 14a of a valve plate 14 which is properly secured at the internal forward portion of the housing 4. a

The valve plate 14 is provided with a high pressure slot 141 and a low pressure slot 142 as shown in FIG. 3, connected to cylinder ports 51 formed in the cylinder barrel 5, for suction and discharge operation of pressure fluid. Loosely engaged on the drive shaft 14 is the valve plate 1, of which the spherical face 14b has its center on the axial center of the drive shaft 1 at the cylinder barrel side and has sliding or oscillating contact with the spherical seat 4a provided at the internal forward portion of the housing 4.

Compensating pistons 15 and 16 are respectively snugly engaged in bores 17 and 18 made in the right and left walls of the housing 4, and the top portions 15a and 16a of these pistons are in precise angle contact with the outer round edge of the valve plate 14. High pressure fluid is supplied to the bore 17 through a conduit 20 from the high pressure slot 141 of the valve plate 14, and low pressure fluid to the bore 18 through a conduit 21 from the low pressure slot 142 of the valve plate 14. The compensating pistons 15 and 16 urge the outer round edge of the valve plate 14 in accordance with the fluid pressure of working fluids supplied into the bores 17 and 18. A numeral 143 indicates a thrust pad made on the face 14a of the valve plate 14, a numeral 144 shows an outer land and a numeral 145 shows an inner land.

When the device, as mentioned above, is operated as a pump, external means, such as a motor, turbine, or the like, is provided to rotate the drive shaft 1 which, in turn, rotates the the cylinder barrel 5. Frictional engagement of the piston shoes 8 on the inclined swash plate Q starts the pumping action by reciprocating the pistons 7 in the pumping chambers 6 of the cylinder barrel 5. In this manner, low pressure fluid is supplied into the pumping chambers 6 from the low pressure slot 142 of the valve plate 14 and consequently discharged at a higher pressure from said pumping chamber 6 into the high pressure slot 141 of the valve plate 14. At the same time, the cylinder barrel 5 rotates with its contacting face 5a urged slidably onto the face 14a of the valve plate 14 by the biasing coil spring 13. In this operation, the valve plate 14 has sliding or oscillating movements along the spherical seat 4a to keep smooth and uniform contact between the valve plate face 14a and the cylinder barrel face 5a the tilting motions of the cylinder barrel face 50 caused by accidental errors in the manufacturing and assembling of the cylinder barrel 5 and the valve plate 14, or the bending of the drive shaft 1 in high pressure operation. The high pressure fluid between the valve plate face 14b and the spherical seat 4a of the housing 4 produces unbalancing or tilting moment on the valve plate face 14b to press it toward the low pressure side. The valve plate 14 is urged by the compensating pistons 15 and 16 at the low and high pressure sides on the outer round edge thereof, said piston 15 at the low pressure side compensating the tilting moment with a thrust force higher than on the piston 16 to urge the valve plate 14 toward the high pressure side. This thrust force on the piston 15 is caused by the high pressure fluid supplied from the high pressure slot 141 through the conduit 20.

Thus, the device can maintain proper fluid sealing on the co-acting surfaces of the cylinder barrel 5 and the valve plate 14, the sliding contacts of the cylinder barrel face 5a with the valve plate face 14a being automatically adjusted by sliding or oscillating motions of the valve plate 14 relative to the tilt of the cylinder barrel face 5a and also by the biasing operation of the compensating pistons 15 and 16 in proportion to the high and low fluid pressures respectively. The compensating piston 16 operates to move the valve plate as described above for piston 15 when the high and low pressure sides are reversed on the valve plate 14.

As shown in FIG. 4, four of compensating pistons 151, 152, 161 and 162 may be mounted in the housing 4, the pistons 151 and 152 being symmetrically positioned about the round edge of the valve plate 14 at the low pressure side and operable with the high pressure fluid supplied from the high pressure slot 141. Other pistons 161 and 162 are symmetrically positioned on the outer round edge of the valve plate 14 at the high pressure side and operable to prevent tilting when the high and low pressure sides are reversed on the valve plate 14.

Another embodiment of this invention is shown in FIGS. 5 and 6; all other details of the device are same as those of the first embodiment except the shape and structure of the valve plate 140, the assembling construction of the valve plate with the housing 40 and the cylinder barrel 50, and the mounting structure of the compensating pistons.

In this embodiment, the contacting face 50a of the cylinder barrel 50 is formed as a spherical seat with the center on the axial center of the drive shaft at the valve plate 140 side. The co-acting surface 140a of the valve plate 140 is also formed in a corresponding spherical shape to the spherical seat 50a so that the valve plate 140 has sliding or oscillating movements with its face 14% as a guide in planar contact with the housing 40 in accordance with the movements of the cylinder barrel face 50a. The compensating pistons 150, 151 and 152, and also 160, 161 and 162 are snugly engaged respectively in bores 170, 171 and 172, and also 180, 181 and 182 made on the right and left walls of the housing 4 and keep their top portions a, 151a, 152a, a, 161a and 162a in precise-angle contact with the outer round edge of the valve plate 140. High pressure fluid is supplied to the bores 170, 171 and 172 through a conduit 20 from the high pressure slot 141 of the valve plate 140 and low pressure fluid to the bores 180, 181 and 182 through a conduit 21' from the low pressure slot 142' of the valve plate 140. The compensating pistons 150, 151, 152, 160, 161 and 162 urge the outer round edge of the valve plate 140 in accordance with the fluid pressure of working fluid supplied in the bores 170, 171, 172, 180, 181 and 182.

When the device in this second embodiment, as mentioned above, is operated as a pump, external means, such as a motor, turbine, or the like, is provided to rotate the drive shaft 1 which, in turn, rotates the cylinder barrel 50. Frictional engagement of the piston shoes 8 on the inclined swash plate 9 starts the pumping action by reciprocating the pistons 7 in the pumping chambers 6 of the cylinder barrel 50. In this manner, low pressure fluid is supplied into the pumping chambers 6 from the low pressure slot 142' of the valve plate 140 and consequently the low pressure slot 142 of the valve plate 140 and consequently discharged at a higher pressure from the pumping chambers 6 into the high pressure slot 141 of the valve plate 140. At the same time, the cylinder barrel 50 makes its rotation with its contacting face urged slidably onto the face 140a of the valve plate 140 by the biasing coil spring 13. During this operation, the valve plate 140 maintains its closely contacting position between the spherical seat 50a of the cylinder barrel 50 and the housing 40 by the thrusting force of the cylinder barrel 50, the urging force of the compensating pistons 150, 151 and 152, and the pressure of the high pressure fluid in the cylinder port 510 in the cylinder barrel 50. This enables the suction and discharge operation between the spherical face 50a of the cylinder barrel 50 and the spherical face 14011 of the valve plate 140, keeping in constant close contact therewith. The valve plate 140 has sliding or oscillating movements in accordance with the movements of the spherical face 50a of the cylinder barrel 50 to keep smooth and uniform contact between the valve plate face 140a and the cylinder barrel face 50a against the tilting motions of the cylinder barrel face 50a caused by the accidental errors in the manufacturing and assembling works of the cylinder barrel 50 and the valve plate 140. With a device of a larger size of the cylinder barrel or in high speed or high pressure operations of the device, when the cylinder barrel is apt to oscillate, the high pressure fluid between the high pressure side of the spherical face 140a of the valve plate 140 and the corresponding portion of the cylinder barrel face 50a produces unbalancing or tilting moment to press the valve plate 140 to the low pressure side. This tilting moment is compensated by the thrust force of the compensating pistons 150, 151 and 152 urged by the high pressure fluid, so that the sliding contact of the cylinder barrel 50 with the valve plate 140 can smoothly be maintained. The compensating pistons 160, 161 and 162 similarly compensate when the high and low pressure sides are reversed on the valve plate 140.

Another embodiment of this invention is shown in FIGS. 7 and 8; all other details of the device are same as those of the first embodiment except the shape and structure of the valve plate 140', the assembling construction of the valve plate 140' with the housing 40 and the cylinder barrel 50', and the mounting structure of the compensating pistons.

In this embodiment, the contacting face 50'a of the cylinder barrel 50 is formed as a spherical seat with the center on the axial center of the drive shaft 1 at the inclined swash plate 9 side. The contacting face l40'a of the valve plate 140 is also formed in a corresponding spherical shape to said spherical seat 50'a so that the valve plate 140 has sliding or oscillating movements with its face 140b as a guide in planar contact with the inner face in the housing 40 in accordance with the movements of the cylinder barrel face 50'a. The compensating pistons 150 and 160 are snugly engaged in bores 170' and 180' made in radial direction within the valve plate 140 and respectively connected with the high pressure slot 141" and the low pressure slot 142 of the valve plate 140. The top rounded portions 150'a and l60'a of said pistons are kept in precise-angle contact with the inner circular wall 40a of the housing 40. High pressure fluid is supplied to the bore 170 from the high pressure slot 141 of the valve plate 140' and low pressure fluid to the bore 180 from the low pressure slot 142" of the valve plate 140. The compensating pistons 150 and 160' press against the inner wall 40a of the housing 40' in accordance working fluid supplied in the bores 170' and 180.

When the device in this third embodiment, as described above, is operated as a pump, external means, such as a motor, turbine, or the like, is provided to rotate the drive shaft 1 which, in turn, rotates the cylinder barrel 50'. Frictional engagement of the piston shoes 8 on the inclined swash plate 9 starts the pumping action by reciprocating the pistons 7 in the pumping chambers 6 of the cylinder barrel 50. In the manner, low pressure fluid is supplied into the pumping chambers 6 from the low pressure slot 142" of the valve plate 140 and consequently discharged at a higher pressure from said pumping chambers 6 into the high pressure slot 141" of the valve .plate 140. At the same time, the cylinder barrel 50 makes its rotation with its contacting face urged slidably onto the face 140'a of the valve plate 140 by the biasing coil spring 13. During this operation, the valve plate 140 maintains its closely contacting position between the spherical seat 50'a of the cylinder barrel 50 and the housing 40' by the thrusting force of the cylinder barrel 50', the counter-urging force of the compensating piston 150 biased onto the inner wall 40' a of the housing 40, and the pressure of the high pressure fluid in the cylinder port 510 in the cylinder barrel 50. This enables the suction and discharge operations of the fluid without undue loss between the spherical face 50'a of the cylinder barrel 50 and the spherical face 140a of the valve plate 140', which remain in constant close contact. The valve plate 140' has sliding or oscillating movements in accordance with the movements of the spherical face 50'a of the cylinder barrel 50' to keep smooth and uniform contact between the valve plate face l40'a and the cylinder barrel face 50'a, and to maintain the most desirable fluid sealing against the tilting motions of the cylinder barrel face 50'a caused by the accidental errors in the manufacturing and assembling of the cylinder barrel 50 and the valve plate 140. With a device of a larger size of the cylinder barrel, or in high speed or high pressure operations of the device, when the cylinder barrel is apt to oscillate, the higher pressure fluid between the high pressure side of the spherical face 140a of the valve plate 140 and the corresponding portion of the cylinder barrel face 50'a produces unbalancing or tilting moment to press the valve plate 140' toward the high pressure side. This tilting moment is compensated by the counteracting force of the piston 150' urged by the high pressure fluid, so that the sliding and continuous contact of the cylinder barrel 50' over its entire surface with the valve plate 140 is smoothly maintained. The compensating piston 160' operates similarly when the high and low pressure sides are reversed on the valve plate Paticularly in this embodiment in which the compensating pistons are engaged inside the housing, such advantages are to be described as the device can be constructed to make the housing rotate or more precise assembling can be realized.

FIG. 9 illustrates another embodiment of this invention; all other details of the device are same as those of the first embodiment except the shape and construction of the valve plate 140", the assembling construction of the valve plate 140" with the housing 40", and the mounting structure of the compensating pistons.

In this embodiment, the valve plate 140 is provided with the high pressure slot 141" and the low pressure slot 142' both of which are connected to the cylinder ports 51 formed in the cylinder barrel 5. The face 1440"b of the valve plate 140" is formed in a spherical shape with the center on the axial center of the drive shaft 1 at the side opposite the cylinder barrel 5 to conduct sliding contact with the spherical seat 40"a of the housing 40". The valve plate 140" is loosely engaged on the drive shaft 1 to have sliding or oscillating contact with the spherical seat 40"a of the housing 40 in accordance with the movements of the cylinder barrel face 5a. The compensating pistons and are engaged in the bores and made within the valve plate 140 along the a diameter and respectively connected with the high pressure slot 141" and the low pressure slot 142" of the valve plate 140". The rounded portions 150" a and l60"a of the pistons are kept in precise-angle, or is supplied with the bore is l70"l60"180 inner wall 40"b of the housing 40". High pressure fluid is supplied to the bore770" from the high pressure slot 141' of the valve plate 140" and low pressure fluid to the bore 180" from the low pressure slot 142' of the valve plate 140". The compensating pistons 150" and 16" press against the inner wall 40"b of the housing 40" in accordance with the pressure of working fluid supplied in the bores 170 and 180".

When the device in this forth embodiment, as described above, is operated as a pump, the drive shaft 1 externally energized rotates the cylinder barrel urged toward the valve plate face 140"a by the biasing coil spring 13, and the valve plate 140 conducts suction and discharge operations maintaining its closely contacting position between the cylinder barrel face 5a and the spherical seat 40"a of the housing 40 by the thrusting force of the cylinder barrel 5, the counteracting force of the compensating piston 150" biased into the inner wall 40"b of the housing 40", and the pressure of the high pressure fluid in the cylinder port 51 of the cylinder barrel 5. Thus, in case the sliding contact between the cylinder barrel face 5a and the valve plate face 140"a is unbalanced by the accidental errors in making of the cylinder barrel 5 and/or the valve plate 140" in the manufacturing and assembling works, the valve plate 140", guided by the spherical seat 40"a of the housing 40", moves in accordance with. the movements of the cylinder barrel face 5a to keep constantly close and uniform continuous contact between the cylinder barrel face 5a and the valve plate face l40a. With a device having a larger cylinder barrel, or in high speed or high pressure operations of the device, when the cylinder barrel is apt to oscillate, the high pressure fluid between the high pressure side of the spherical face 140"a of the valve plate 140" and the corresponding portion of the spherical seat 40"a of the housing 40" produces unbalancing or tilting moment to press the valve plate toward the high pressure side. This tilting moment is compensated by the counteracting force of the compensating piston 150" pressing against the inner wall 40"b of the housing 40" by the high pressure fluid, so that the sliding contact of the cylinder barrel 5 with the valve plate 140" is smoothly maintained. The compensating piston 160" operates similarly when the high and low pressure sides are reversed on the valve plate 140 The compensating pistons are shown one each on the right and left sides of the valve plate in the referred figure, however, it is very obvious that a plural number of the pistons can be installed in symmetrical positions on the high pressure and low pressure sides of the valve plate 140' What is claimed is:

1. A rotary pump or motor for use with externally supplied fluid comprising, a housing, a drive shaft joumaled in said housing, a barrel rotatable with said drive shaft and mounted within said housing so as to be slidable axially along the drive shaft, said barrel having a plurality of axial pumping chambers each with a port, an axially reciprocating piston in each of said pumping chambers, an inclined swash plate slidably seating one end of said pistons for reciprocating said pistons while said barrel is being rotated, an annular valve plate having a plane surface and an opposite surved surface slidably interposed between the forward end surface of said barrel and the internal forward wall surface of said housing and radially oscillatable in accordance with tilting moments acting on said barrel, means biasing said barrel forwardly toward the valve plate, high and low pressure fluid passages in said valve plate extending between said plane and curved surfaces and which communicate with the interior of said pumping chambers through said ports during a portion of each revolution of the barrel, the cross sectional area presented along each of said fluid passages, because of the curved surface of the valve plate, being such as to exert a greater unbalancing force tending to move the valve plate in one direction radially of the valve plate than the other and compensating means for offsetting said unbalancing force, said compensating means including at least one balancing piston radially slidable in a cooperating bore connected to receive pressure fluid from said high pressure passage of the valve plate, said bore being radially formed in one of said housing and valve plate, and said balancing piston being urged against the other of said housing and valve plate to exert a pressure for moving the valve plate toward the counterdirection of said unbalancing force.

2. The rotary pump or motor of claim 1, wherein said valve plate has a circular shape, said balancing piston being mounted in said cooperating bore formed in said housing with the axes of the piston and bore aligned in a radial direction of the valve plate.

3. The rotary pump or motor of claim 1, wherein said balancing piston is mounted in said cooperating bore formed in said valve plate with the axes of the piston and bore aligned in a radial direction of the valve plate.

4. A rotary pump or motor as claimed in claim 1, wherein said valve plate has a planar surface in sliding contact with the adjacent forward face of the barrel which is also planar, the opposite surface of the valve plate being spherical and complementing a spherical seat provided on the internal forward wall of said housing for smooth sliding contact therewith, said valve plate being radially oscillatable on said spherical seat as a guide.

5. A rotary pump or motor as claimed in claim 4, wherein said spherical coacting surfaces of the valve plate and the housing are convex in the forward direction facing away from said planar barrel surface.

6. A rotary pump or motor is claimed in claim 4, wherein said spherical coacting surfaces of the valve plate and the housing are convex in the rearward direction facing toward said planar barrel surface.

7. A rotary pump or motor as claimed in claim 1, wherein said valve plate has a spherical surface in sliding contact with a complementary spherical surface provided on the adjacent forward face of the barrel which is also spherical, the opposite surface of the valve plate being planar and in sliding contact with a planar forward wall surface of said housing, said valve plate being radially oscillatable along said spherical coacting surfaces.

8. A rotary pump or motor as claimed in claim 7, wherein said spherical coacting surfaces of the valve plate and the barrel are convex in the rearward direction facing away from said planar forward wall surface of the housing.

9. A rotary pump or motor as claimed in claim 7, wherein said spherical coacting surfaces on the valve plate and barrel are convex in the forward direction faced toward said forward planar surface of the housing.

10. A rotary pump or motor as claimed in claim 2, wherein said compensating means comprise at least one pair of bores provided symmetrically in the wall of the housing, the axial direction of each bore being aligned with a radius of the valve plate, and a balancing piston operably disposed in the axial direction of and within each of said bores and having a protruding end which engages the circular periphery of the valve plate.

11. A rotary pump or motor as claimed in claim 10, wherein one of said bores or each pair is connected to the high pressure fluid passage in the valve plate and the other bore of each pair is connected to the low pressure fluid passage.

12. A rotary pump or motor as claimed in claim 3, wherein said balancing piston has a protruding end which engages the internal wall surface of said housing.

13. A rotary pump or motor as claimed in claim 3, wherein said compensating means comprise at least one pair of bores provided symmetrically in said valve plate, the axial direction of each bore being aligned with a radius of the valve plate, and a balancing piston operably disposed in the axial direction of and within each of said bores and having a protruding end which engages the internal wall surface of said housing.

14. A rotary pump or motor as claimed in claim 13, wherein one of said bores of each pair is connected to the high pressure passage in the valve plate and the other bore of each pair is connected to the low pressure fluid passage. 

1. A rotary pump or motor for use with externally supplied fluid comprising, a housing, a drive shaft journaled in said housing, a barrel rotatable with said drive shaft and mounted within said housing so as to be slidable axially along the drive shaft, said barrel having a plurality of axial pumping chambers each with a port, an axially reciprocating piston in each of said pumping chambers, an inclined swash plate slidably seating one end of said pistons for reciprocating said pistons while said barrel is being rotated, an annular valve plate having a plane surface and an opposite surved surface slidably interposed between the forward end surface of said barrel and the internal forward wall surface of said housing and radially oscillatable in accordance with tilting moments acting on said barrel, means biasing said barrel forwardly toward the valve plate, high and low pressure fluid passages in said valve plate extending between said plane and curved surfaces and which communicate with the interior of said pumping chambers through said ports during a portion of each revolution of the barrel, the cross sectional area presented along each of said fluid passages, because of the curved surface of the valve plate, being such as to exert a greater unbalancing force tending to move the valve plate in one direction radially of the valve plate than the other and compensating means for offsetting said unbalancing force, said compensating means including at least one balancing piston radially slidable in a cooperating bore connected to receive pressure fluid from said high pressure passage of the valve plate, said bore being radially formed in one of said housing and valve plate, and said balancing piston being urged against the other of said housing and valve plate to exert a pressure for moving the valve plate toward the counterdirection of said unbalancing force.
 2. The rotary pump or motor of claim 1, wherein said valve plate has a circular shape, said balancing piston being mounted in said cooperating bore formed in said housing with the axes of the piston and bore aligned in a radial direction of the valve plate.
 3. The rotary pump or motor of claim 1, wherein said balancing piston is mounted in said cooperating bore formed in said valve plate with the axes of the piston and bore aligned in a radial direction of the valve plate.
 4. A rotary pump or motor as claimed in claim 1, wherein said valve plate has a planar surface in sliding contact with the adjacent forward face of the barrel which is also planar, the opposite surface of the valve plate being spherical and complementing a spherical seat provided on the internal forward wall of said housing for smooth sliding contact therewith, said valve plate being radially oscillatable on said spherical seat as a guide.
 5. A rotary pump or motor as claimed in claim 4, wherein said spherical coacting surfaces of the valve plate and the housing are convex in the forward direction facing away from said planar barrel surface.
 6. A rotary pump or motor is claimed in claim 4, wherein said spherical coacting surfaces of the valve plate and the housing are convex in the rearward direction facing toward said planar barrel surface.
 7. A rotary pump or motor as claimed in claim 1, wherein said valve plate has a spherical surface in sliding contact with a complementary spherical surface provided on the adjacent forward face of the barrel which is also spherical, the opposite surface of thE valve plate being planar and in sliding contact with a planar forward wall surface of said housing, said valve plate being radially oscillatable along said spherical coacting surfaces.
 8. A rotary pump or motor as claimed in claim 7, wherein said spherical coacting surfaces of the valve plate and the barrel are convex in the rearward direction facing away from said planar forward wall surface of the housing.
 9. A rotary pump or motor as claimed in claim 7, wherein said spherical coacting surfaces on the valve plate and barrel are convex in the forward direction faced toward said forward planar surface of the housing.
 10. A rotary pump or motor as claimed in claim 2, wherein said compensating means comprise at least one pair of bores provided symmetrically in the wall of the housing, the axial direction of each bore being aligned with a radius of the valve plate, and a balancing piston operably disposed in the axial direction of and within each of said bores and having a protruding end which engages the circular periphery of the valve plate.
 11. A rotary pump or motor as claimed in claim 10, wherein one of said bores or each pair is connected to the high pressure fluid passage in the valve plate and the other bore of each pair is connected to the low pressure fluid passage.
 12. A rotary pump or motor as claimed in claim 3, wherein said balancing piston has a protruding end which engages the internal wall surface of said housing.
 13. A rotary pump or motor as claimed in claim 3, wherein said compensating means comprise at least one pair of bores provided symmetrically in said valve plate, the axial direction of each bore being aligned with a radius of the valve plate, and a balancing piston operably disposed in the axial direction of and within each of said bores and having a protruding end which engages the internal wall surface of said housing.
 14. A rotary pump or motor as claimed in claim 13, wherein one of said bores of each pair is connected to the high pressure passage in the valve plate and the other bore of each pair is connected to the low pressure fluid passage. 